Illinois Statutes Chapter 815. Business Transactions § 137/80. Late payment fee

(1) the late payment fee shall not be in excess of 4% of the amount of the payment past due;

(2) the late payment fee shall only be assessed for a payment past due for 15 days or more;

(3) the late payment fee shall not be imposed more than once with respect to a single late payment;

(4) a late payment fee that the lender has collected shall be reimbursed if the borrower presents proof of having made a timely payment; and

(5) a lender shall treat each payment as posted on the same business day as it was received by the lender, servicer, or lender's agent or at the address provided to the borrower by the lender, servicer, or lender's agent for making payments.